As shown in FIGS. 1-3, the U.S. Pat. No. 4,677,837 discloses a thread rolling machine comprising an adjustment structure of the fixed mold thereof. The adjustment structure comprises a split thread line, a blind angle, a rolling depth, and an angle of inclination. The split thread line refers to a first slide plate 2 mounted on a machine frame 1 such that the first slide plate 2 is pushed by a threaded rod 3 to move back and forth so as to actuate the thread line of the split movable mold 5 of the fixed mold 4. The blind angle refers to a second rotary plate 6 mounted on the first slide plate 2 such that the second rotary plate 6 is pushed by a threaded rod 7 mounted on the first slide plate 2 to rotate along the first slide plate 2, thereby actuating the fixed mold 4 to adjust the feed angle with the movable mold 5. A third slide plate 8 is mounted on the second rotary plate 6 such that the third slide plate 8 is pushed by a threaded rod 9 of the second rotary plate 6 to move along the left and the right of the second rotary plate 6, thereby actuating the fixed mold 4 to adjust the distance between the fixed mold 4 and the movable mold 5 so as to provide the blank with a required roll depth. The third slide plate 8 is provided with an arcuate machine frame 10 mounted thereon. A slide block 11 is connected with a U-shaped plate 12 which is fastened with the fixed mold 4. The fixed mold 4 is drawn to swivel for adjusting the parallel degree relative to the movable mold 5, so as to attain consistency of the thread form.
In view of the second rotary plate 6 being mounted on the first slide plate 2 for the adjustment of the blind angle, a greater degree of freedom is resulted from the pushing and the turning. As a result, the rigidity is poor. The rotational force on the fixed mold may result in the stress destruction of the second rotary plate 6 and the threaded rod 7. As a result, the adjustment precision is compromised.